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Hardware Arduino HID instead of the OTG

Using Arduino HID on non-v0 platforms is useful if you need a simple and primitive keyboard/mouse emulation device. For example, when used with a hardware KVM switch wich does not recognize composite HID. You can use the Arduino HID firmware to emulate (at your choice):

USB keyboard & mouse

  • Build and connect HID according to the diagram (the bottom part with transistor, level-shifter and Arduino).
  • Switch to RW-mode using command rw.
  • Add these lines to /etc/kvmd/override.yaml (remove {} in the file before): 
    kvmd:
    hid:
        type: serial
        reset_pin: 4
        device: /dev/kvmd-hid
  • Create file /etc/udev/rules.d/99-kvmd-extra.rules: 
    KERNEL=="ttyAMA0", SYMLINK+="kvmd-hid"
  • Run systemctl disable [email protected].
  • Remove console=ttyAMA0,115200 and kgdboc=ttyAMA0,115200 from /boot/cmdline.txt.
  • Flash the Arduino HID.
  • Run reboot.

PS/2 keyboard

Using the PS/2 firmware currently has the following limitations:

  • The possibility of using USB HID is excluded.
  • PS/2 mouse is not supported due to features of the PS/2 protocol.

Both of these problems will be solved one way or another in the future and the two different firmware versions will be combined into one universal one.

To select the PS/2 firmware, you need to follow the instructions for USB, but with one exception. At the device firmware stage instead of commands:

# make
# make install

Use commands:

# make ps2
# make install

Next, you need to connect the Arduino pins to the female PS/2 port of your motherboard. Choose the purple port. If your motherboard only have one port, it's probably universal and can be used either for the keyboard or for the mouse. Most likely, it is painted in two colors: green and purple. You can use it either.

Follow this diagram:

Female PS/2 port (front view) Pinout
drawing Arduino pin 7 <-> PS/2 CLOCK
Arduino pin 5 <-> PS/2 DATA
Arduino GND pin <-> PS/2 GND

Connect VIN pin of Arduino to any Raspberry's 5v pin.

PS/2 keyboard & USB mouse

This is a mixed mode of HID which is a compromise for old computers. Connections are made simultaneously by both USB and PS/2 pins, as shown in the diagram above. Follow the PS/2 instructions, but use these commands to build and install the firmware:

# make mixed
# make install

You don't need to connect the Arduino VIN pin if you connected USB (the Arduino will get power through it).